Here's a design for a non-dart paper airplane. This is more of a glider than the dart and will generally fly straighter and slower than the dart type design. It is also a little more difficult to build. So without further ado here are the instructions.

Next fold the paper hoizontally so that each top corner is on top of where the crease on that side meets the edge.

Unfold.

Now, take hold of the two points where the middle crease (the one that's made of dashes) meets the edge and pull them together and down so that they meet at point (i). This should pull the two diagonal creases together so that point (j) is directly on top of (i).

The next three diagrams show a close up on the top part of the glider. This is the most complicated part of contruction but it is necessary if the glider is to hold together in flight.

Take hold of the upper layer at point (a) and fold it up to point (b).

Take hold of the upper layer at point (c) and fold it across to point (d).
What you have at this stage looks like the third diagram. The piece you have just folded across has formed a little horizontal pocket (above "e") and the corner you folded up before that has formed a vertical flap (piece "f").

Take the top of the flap "f", point (g) and tuck it into the pocket so it is completely folded down. This stage is quite intricate but as long as the flap "f" cannot get loose it is good enough.

The final glider should look something like the diagram below from the back. The two diagonal bits are the complicated pieces at the front. They tend to stick up like this but it doesn't affect flight too much. Enjoy!

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|____/_\____|

Another Airplane Design:

This paper airplane design is the simplest I have ever come across. It flies surprisingly well at high speed but can't really glide due to its weight distribution.

Instructions:

Take a piece of A4 or legal size paper or any rectangular piece of paper will do.

If you've used heavy paper that might be it. Test it and if it flies well you don't need to do the next stage.
The reason it doesn't fly well is that the wings aren't stable enough to hold the glider in the air. The solution to this problem is to fold up 1 cm of the wings up on either side.

This will provide the glider with the stability it needs to fly effectively.

To throw the glider you need to grip the front in the middle between your thumb and middle or pointer finger with your palm facing you and throw it by moving your hand away from you. This method takes a little practice but it is a lot more effective than trying to throw it the normal way.

However, to throw this plane correctly, it needs to be pinched at the apex of the middle fold. Done correctly, the plane will look like this from a front view:

\ /\ /\ /
\ / \ / \ /
\/ \/ \/
|_______| |_______|
| |
wing wing

Hints and Tricks

If your plane is diving to the floor, or doing something other than what you want, fix it by adding flaps. Just make two cuts the desired width from each other, and fold up or down, or just fold one. The best place for these flaps is the back of the main wing(the wing you folded first). To boomerang your plane, fold only one flap, or try creating flaps on the side wings(the wings you folded second). There are so many things you can do to this plane, and get funny, wild, or spectacular results. Try throwing the plane differently. I discovered that you can throw the plane backwards, and it will flip upside-down and fly forward. To do this, you put your index finger inside the middle crease with the plane facing you. Then put your thumb on the other side of the paper, underneath the plane, and your middle finger the same place on the other side. To throw, flick your wrist downward, letting the plane go when it is pointing at the floor. As I said before, this plane is very versatile. Use your imagination, and go crazy! Please /msg me any problems or tricks you have discovered.